Effect of MgCl2 on electrophoretic deposition of TbF3 powders on Nd-Fe-B sintered magnet

Abstract

Using electrophoretic deposition (EPD) method, the TbF3 powders were deposited on the surface of sintered Nd-Fe-B magnets, and the effects of MgCl2 on electrophoretic deposition and grain boundary diffusion were investigated. The results show that addition of 5 wt% MgCl2 can significantly improve the EPD efficiency and improve the adhesion of the coating by releasing local stress through the formation of special gully morphology. Combining with Biesheuvel equation, the effects of suspension concentration, voltage and time on EPD amount were studied. The Biesheuvel equation can be simplified as γ = AUSct/L, and A (= 0.0141–0.0144) in this experiment was calculated to achieve the quantitative calculation of EPD amount. After heat treatment of 875 °C × 10 h + 500 °C × 1 h, the coercivity of 48H (7 mm) sintered magnet with 0.3 wt% TbF3 increases from 18.5 to 22.4 kOe, with an increase of 21.1%. The core–shell structure was observed by a back-scattered scanning electron microscope (BSE-SEM), which proves that the addition of MgCl2 has no adverse effect on the grain boundary diffusion of Nd-Fe-B sintered magnets.